Wireless networks are becoming ubiquitous in society. Wireless subscribers use a wide variety of wireless devices, including cellular phones, personal communication services (PCS) devices, and wireless modem-equipped personal computer (PCs), among others. These devices are used to access both public and private networks. To maximize usage of the available bandwidth, wireless networks implement a number of multiple access technologies to allow more than one subscriber to communicate simultaneously with each base station (BS) in a wireless system. These multiple access technologies include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA). These technologies assign each system subscriber to a specific traffic channel that transmits and receives subscriber voice/data signals via a selected time slot, a selected frequency, a selected unique code, or a combination thereof.
Most wireless network architectures generally consist of a number of geographically dispersed base stations that provide wireless communications in a designated coverage area served by a wireless service provider. Groups of base stations are connected by land lines to a common mobile switching center (MSC) that provides high-level control over the group of base stations and connects the base stations to the public switched telephone network (PSTN). Each base station (BS) covers a particular geographic area (or cell) and may be comprised of one or more base transceiver stations and a base station controller (BSC).
Base station controllers and base transceiver stations are well known to those skilled in the art. A base station controller is a device that manages wireless communications resources, including the base transceiver stations, for specified cells within a wireless communications network. A base transceiver station comprises the RF transceivers, antennas, and other electrical equipment located in each cell site. This equipment may include air conditioning units, heating units, electrical supplies, telephone line interfaces, and RF transmitters and RF receivers.
A common feature of many conventional CDMA wireless network architectures is the combining or commingling of radio dependent (RF dependent) functions and radio independent (RF independent) functions within a single control system in the BS/MSC interface. This single control system is sometimes referred to as a selection and distribution unit (SDU) and it may be located within the BS, within the MSC, or intermediate the BS and the MSC. The radio dependent functions of an SDU include CDMA power control functions, diversity functions to support CDMA soft handoff (i.e., selection and distribution), radio link protocol (RLP) and multiplexing and de-multiplexing of voice and/or data traffic. The radio independent functions of an SDU include vocoding and transcoding, IP router for Internet packet data and modem pools for circuit data and fax applications.
There are drawbacks, however, in any network architecture that combines radio dependent and radio independent functions together in a single SDU or equivalent control system. The location of the SDU can create incompatibilities in architectures that use components from different vendors. For example, if vendor A places SDU functions in its MSC (but not in its BS) and vendor B places SDU functions in its BS (but not in its MSC), a wireless network operator would not be able to build a network using an MSC from vendor B and a BS from vendor A, since neither contains an SDU. This also means that if components in a wireless network are being replaced or retrofitted, the network operator can buy equipment only from vendors who install the SDU functionality in locations compatible with the other equipment in the wireless network.
There is therefore a need in the art for an improved CDMA wireless network architecture that is less susceptible to incompatibilities between the equipment of different vendors. In particular, there is a need in the art for a CDMA architecture that does not combine radio dependent and radio independent functions in a single system.